Bonding system and method for using the same

Abstract

A method includes mounting a first wafer on a first wafer chuck and mounting a second wafer on a second wafer chuck. The second wafer is brought into physical contact with the first wafer. A relative distance between the first wafer and the second wafer is monitored using a distance sensor. A pressure of a vacuum zone on the second wafer chuck is controlled using feedback from the distance sensor. The bonded first wafer and second wafer are removed from the first wafer chuck.

What is claimed is: 
     
       1. A method comprising:
 mounting a first wafer on a first wafer chuck and mounting a second wafer on a second wafer chuck; 
 bringing the second wafer into physical contact with the first wafer; 
 monitoring a first relative distance between the first wafer and the second wafer using a first distance sensor in a first area above the first distance sensor, and monitoring a second relative distance between the first wafer and the second wafer using a second distance sensor in a second area above the second distance sensor, wherein the first relative distance is smaller than the second relative distance, wherein each distance sensor measures intensity peaks at a plurality of interfaces to determine the respective relative distances, and wherein changes in the measured relative distances over time indicate propagation of a bonding wave between the first and second wafers; 
 independently controlling levels of applied vacuum of a first vacuum zone and a second vacuum zone on the second wafer chuck using feedback from the first distance sensor and the second distance sensor, wherein the first vacuum zone is above the first area and the second vacuum zone is above the second area, and wherein responsive to the changes in the measured relative distances indicating non-uniform bonding wave propagation, the level of applied vacuum of the first vacuum zone is increased and the level of applied vacuum of the second vacuum zone is decreased to compensate for detected variations in bonding wave velocity; and 
 removing the bonded first wafer and second wafer from the first wafer chuck. 
 
     
     
       2. The method of  claim 1 , wherein the first distance sensor and the second distance sensor are infrared interferometers. 
     
     
       3. The method of  claim 1 , wherein the first distance sensor and the second distance sensor are mounted beneath the first wafer chuck. 
     
     
       4. The method of  claim 1 , wherein the decreased level of applied vacuum of the second vacuum zone accelerates a local velocity of a bonding wave between the first wafer and the second wafer in the second area. 
     
     
       5. The method of  claim 1 , wherein the increased level of applied vacuum of the first vacuum zone decelerates a local velocity of a bonding wave between the first wafer and the second wafer in the first area. 
     
     
       6. The method of  claim 1 , wherein bringing the second wafer into physical contact with the first wafer comprises using a push pin extending through the second wafer chuck. 
     
     
       7. A method comprising:
 loading a first wafer and a second wafer into a wafer bonding system, wherein the first wafer is on a top surface of a first wafer chuck and the second wafer is on a bottom surface of a second wafer chuck, wherein the second wafer chuck comprises a first vacuum zone and a second vacuum zone, wherein the first vacuum zone and the second vacuum zone are arranged in a segmented ring pattern; 
 using a push pin to physically contact the second wafer with the first wafer at a first point; 
 modulating a velocity of a first bonding wave between the first wafer and the second wafer using feedback from a plurality of distance sensors, wherein each distance sensor measures intensity peaks at a plurality of interfaces to determine distances between the first and second wafers, the modulating the velocity of the first bonding wave comprising independently controlling pressure levels of the first vacuum zone and the second vacuum zone based on measured changes in the determined distances over time indicating propagation of the first bonding wave, wherein responsive to the measured changes in the determined distances indicating non-uniform bonding wave propagation, the pressure level of the first vacuum zone is increased and the pressure level of the second vacuum zone is decreased to compensate for detected variations in bonding wave velocity; and 
 after the first wafer and the second wafer are bonded, removing the first wafer and the second wafer from the wafer bonding system. 
 
     
     
       8. The method of  claim 7 , wherein the plurality of distance sensors are mounted below the first wafer chuck. 
     
     
       9. The method of  claim 8 , wherein the first wafer chuck is at least partially transparent to infrared light. 
     
     
       10. The method of  claim 7 , wherein before the modulating the velocity of the first bonding wave, the first bonding wave comprises a diamond profile. 
     
     
       11. The method of  claim 7 , wherein after the modulating the velocity of the first bonding wave, the first bonding wave comprises a circular profile. 
     
     
       12. The method of  claim 7 , further comprising:
 after the first bonding wave reaches edges of the first wafer and the second wafer, retracting the push pin; and 
 annealing the bonded first wafer and the second wafer. 
 
     
     
       13. The method of  claim 7 , wherein the push pin extends through the second wafer chuck, and wherein an infrared light source is disposed adjacent the push pin in the second wafer chuck. 
     
     
       14. A method comprising:
 placing a first wafer on a first wafer chuck and placing a second wafer on a second wafer chuck; 
 bringing a first portion of the second wafer into physical contact with the first wafer; 
 monitoring distances between the first wafer and the second wafer at a plurality of locations using a plurality of infrared distance sensors on the first wafer chuck, wherein each infrared distance sensor measures intensity peaks at a plurality of interfaces to determine distances between the first and second wafers; 
 independently adjusting pressure levels of a plurality of vacuum zones on the second wafer chuck using feedback from the plurality of infrared distance sensors, wherein the plurality of vacuum zones comprise a first vacuum zone and a second vacuum zone, wherein the first vacuum zone and the second vacuum zone are spaced apart from a center of the second wafer chuck by a same distance, wherein responsive to measured changes in the determined distances indicating non-uniform bonding wave propagation, a pressure level of the first vacuum zone is increased and a pressure level of the second vacuum zone is decreased to compensate for detected variations in bonding wave velocity; and 
 removing the bonded first wafer and second wafer from the first wafer chuck. 
 
     
     
       15. The method of  claim 14 , wherein the first wafer is separated from the plurality of infrared distance sensors by the first wafer chuck, and wherein the first wafer chuck is at least partially transparent to infrared light. 
     
     
       16. The method of  claim 14 , wherein the second wafer chuck further comprises an infrared light source with an output wavelength larger than 1.1 μm. 
     
     
       17. The method of  claim 14 , wherein the plurality of infrared distance sensors are low-coherence interferometry infrared sensors. 
     
     
       18. The method of  claim 14 , wherein the plurality of distance sensors are uniformly distributed in angular directions with respect to a top surface of the first wafer chuck. 
     
     
       19. The method of  claim 18 , wherein the plurality of distance sensors are uniformly distributed in radial directions with respect to the top surface of the first wafer chuck. 
     
     
       20. The method of  claim 14 , wherein bringing the first portion of the second wafer into physical contact with the first wafer comprises using a push pin extending through the second wafer chuck.